The present invention relates to a power shift transmission having two transmission paths, a separate friction clutch being assigned to each transmission path and the transmission paths being coupleable to an output shaft for torque transmission. The invention also relates to a method for the control of a push downshift of a power-shift transmission having two transmission paths.
The aforementioned powershift transmission is a transmission provided for use in a motor vehicle and having two transmission paths. The actuation of the individual transmission paths during the shifting process and the actuation of the friction clutches may be accomplished via electromechanical and/or hydraulic actuators. Cited as a special embodiment of such a dual clutch transmission is a so-called parallel shift gearbox (PSG) in which the individual gears are disposed in two transmission elements, the two aforementioned transmission paths, each transmission path having its own friction clutch for torque engagement.
A parallel shift gearbox of this type is powershiftable to prevent an interruption of tractive force during the shifting operation; that is, with it, it is possible to pre-select a gear in the transmission element without a load while the torque is being transmitted by the other transmission element. If the actual shifting operation, that is the cross-fading from one gear to the next, is to occur, the torque is cross-faded from the friction clutch assigned to the active transmission path to the friction clutch assigned to the inactive transmission path.
A great advantage of such a parallel shift gearbox compared to the use of an automatic transmission having a planetary gear is the reduction in fuel consumption of the engine coupled thereto, because an automatic transmission regularly has multiple clutches or brake bands, that produce friction and, thus, a loss of power.
However, in a parallel shift gearbox, the clutch, also configurable as a friction clutch, of the transmission element that is torque-free at that moment produces no slip as long as also no gear is pre-selected in the transmission element.
The requirement profile for such a parallel shift gearbox corresponds to a large extent to that for an automatic transmission; this means that a vehicle equipped with such a parallel shift gearbox is supposed to provide a driving comfort that corresponds to that of a vehicle equipped with a planetary gear.
As already mentioned below, the parallel shift gearbox is powershiftable, which is valid for shifts in pull mode as well as shifts in push mode of the vehicle equipped with it.
An essential criterion regarding a motor vehicle equipped with such a transmission is the prevention, generally speaking, of vibration problems. If then a vehicle is considered in terms of vibration technology in the area of the drive, then vibrations occurring in the area of the engine/transmission/drivetrain chain may contribute to a reduction of the driving comfort experienced by the driver. Therefore, a driver would surely consider judder movements during a gear change operation to be detrimental to driving comfort and similarly would also judge vibrations occurring in the drivetrain to be negative with regard to driving comfort.
Dynamic vibration operations may occur for a parallel shift gearbox during the gear change, for example, also during downshifting operations from, for example, second into first gear during the push mode, thus, for example, when the vehicle is coasting up to a red light.
In tests carried out on the vehicle, it is shown then that such drivetrain vibrations, which are to be avoided, may occur during push downshifts as a consequence of a synchronization jolt.